Attempts have been made to incorporate metallic oxides such as antimony oxide into organic polymers, both natural and synthetic, to improve their properties. For example, these oxides have been used to improve the resistance to burning, particularly when employed in conjunction with organic halogen compounds and other halogen-containing materials. While the exact mechanism which results in the flame-retardant properties is not fully understood, it is believed that an antimony oxide halogen compound may be formed in situ which interferes with oxidizing reactions and therefore inhibits burning.
A variety of techniques have been employed to introduce the antimony oxide into organic polymers. For example, oxide particles prepared by milling have been suspended in spinning solutions, molding solutions, or polymer melts in attempts to incorporate the oxide in the resulting film, fiber or molded body. The use of this technique generally results in delustering of the polymer due to the scattering of light by the large oxide particles, and the large particles also have relatively low chemical reactivity and a low efficiency as a flame proofing agent. In the case of fibers, the diameter of the oxide particles may approach the diameter of the fibers themselves thereby weakening the bond between the organic polymer and the oxide.
Antimony oxides also have been applied as surface coatings along with a resinous binder. These coating techniques, however, also result in delustering and produce fabrics which have a stiff, harsh hand, poor flexibility and low tear strength.
Additional attempts have been made in the art to avoid some of the deficiencies of the above procedures by using aggregates of oxides prepared as gels, as precipitated powders, and as aggregates prepared by oxidizing the corresponding metallic halides. The use of aggregates, however, has resulted in non-uniformity of properties resulting from the difficulties of preparing uniform aggregates and homogenously distributing the aggregates throughout the polymer.
More recently, it has been discovered that antimony oxide prepared as sols of colloidal particles of antimony oxide dispersed in various liquid media is useful. For example, U.S. Pat. No. 3,676,362 describes sols composed of substantially discrete colloidal particles of antimony oxide having an average particle size in the range of about 2 to about 50 millimicrons dispersed in a polar, organic liquid. Such sols can be mixed with a solution of a polymer in a polar organic liquid, and the mixture processed in a conventional manner for making fibers and films. These sols are prepared by reacting a metal halide with water and ammonia in a polar organic liquid. The water converts the halide to antimony oxide in colloidal dispersion and an ammonium salt precipitates.
U.S. Pat. No. 3,860,523 describes the preparation of colloidal antimony oxide sol, preferably in the Sb.sub.2 O.sub.5 form with an average particle diameter of about 2 to 100 millimicrons. The sol is prepared by first preparing water-soluble potassium antimonate by reacting antimony trioxide with potassium hydroxide and hydrogen peroxide in the ratio of 1 mole to 2.1 moles to 2 moles, and thereafter deionizing the potassium antimonate by passing the solution through a hydrogen form cation exchange resin.
Another method for forming sols of antimony pentoxide is described in U.S. Pat. No. 3,657,179. This patent describes the reaction of antimony trichloride with nitric acid to form a dispersion in a polar organic solvent, and stabilizing the dispersion with an alpha-hydroxy carboxylic acid. Such dispersions contain from about 0.01 to 5% water by weight.
Another process for preparing colloidal dispersions of antimony pentoxide is described in U.S. Pat. No. 3,994,825, and the process involves mixing particles of antimony trioxide with an aliphatic polyhydroxy alcohol having vicinal hydroxyl groups and contacting said particles with hydrogen peroxide to convert the antimony trioxide to hydrous antimony pentoxide. Reaction preferably is accomplished at a temperature of between 50.degree. and 105.degree. C. The colloidal sol which results is a stable dispersion containing antimony pentoxide with a reported average size of from about 50 Angstroms to about 200 Angstroms.
More recently, an improved method for preparing colloidal aqueous sols of antimony pentoxide from a water insoluble metal antimonate was described in U.S. Pat. No. 4,110,247. The method involves passing a slurry of a water-insoluble metal antimonate through a fluidized bed containing a cation exchange resin whereby the metal antimonate is converted to a colloidal antimony pentoxide.